1. Field of the Invention
The present invention relates to a separation method and apparatus/system for cleaning of combustion gas followed by the capture and sequestering of carbon dioxide, and more particularly, the present invention relates to a water based separation method and apparatus/system for capturing and sequestering carbon dioxide from combustion gas and other mixtures.
2. Description of Related Art
A major limitation to reducing greenhouse gases in the atmosphere is the expense of stripping carbon dioxide from other combustion gases. Without a cost-effective means of accomplishing this, the world's hydrocarbon resources, if used, will continue to contribute carbon dioxide to the atmosphere.
A few major power plants around the world currently remove carbon dioxide from flue gas, for sale as an industrial product. Oil companies commonly remove carbon dioxide from natural gas to improve its energy content. In both cases the most common technology is temperature-swing absorption (TSA) using a methylated ethyl amine solvent (MEA).
The MEA process relies on the strongly selective bonding of carbon dioxide to the solvent for selective removal from the flue gas, but requires considerable heating to increase the gas pressure in the removal step to an acceptable level. In particular, the flue gas contacts the MEA dissolved in water in a packed column, and then the carbonated solution is heated to 120° C. to extract a nearly pure carbon dioxide gas. Sulfur and nitrous oxide are removed ahead of this step because they bind so tightly to the solvent that they cannot be removed. An alternative MEA cycle using pressure cycling can be used in some cases, when the inlet gas to be separated is at high pressure and the carbon dioxide can be removed from the solvent by lowering the ambient pressure. In both this process and the temperature swing process, the carbon dioxide fugacity is changed by changing the physical conditions of the solvent. This is inefficient due to the energy unrecoverably lost doing work on a large volume of solvent, in addition to the mechanically complex system and the need for frequent solvent addition due to degradation. It is a fundamentally complex and chemically-intensive process only suitable for large-scale industrial separation today and it is too expensive to contribute a globally-large removal of carbon from combustion sources.
The Greenhouse Gas Program of the International Energy Agency (Davison et al. 2001) has studied the application of this technology to electric power plants. They estimate an energy cost of approximately 35% of the power generated by a pulverized coal power plant is required for this type of carbon dioxide removal. Many variants are under study, which permit slightly higher efficiency or longer solvent life, including solid sorbents; thus far, dramatic improvements have not been seen.
Accordingly, a need exists for an improved process and system to control the removal of CO2 in an economical and environmentally safe way. The present invention is directed to such a need.